1. Field of the Invention
The present invention relates to image forming apparatuses employing an electrographic method, such as copiers, printers, facsimiles, and multifunctional machines having these functions. The present invention particularly relates to image forming apparatuses provided with a belt-shaped rotatable member functioning as an intermediate transfer member, a paper transporting member, and the like.
2. Description of Related Art
Conventional examples of image forming apparatuses include ones in which paper is transported by being electrostatically adhered to a belt-shaped or a drum-shaped paper transporting member that rotates in synchronization with an image forming member such as a photoconductive member, and the paper is then separated from the paper transporting member to be sent to a fixing device after a toner image is transferred thereonto from the image forming member. Conventional examples of image forming apparatuses also include ones in which a toner image formed on an image forming member is primarily transferred onto a belt-shaped or a drum-shaped intermediate transfer member that rotates in synchronization with the image forming member, the toner image transferred onto the intermediate transfer member is then transferred at a secondary transfer section onto paper that is fed temporarily adheres to the intermediate transfer member, and the paper is then separated from the intermediate transfer member to be sent to a fixing device. In these image forming apparatuses, paper jams sometimes occur due to the paper onto which an image has been transferred failing to be separated from the paper transporting member or from the intermediate transfer member (which will be collectively called a “belt-shaped rotatable member”) to remain adhered to the belt-shaped rotatable member, or due to abnormal transportation of the paper. For the purpose of detecting occurrence of such paper jams, some conventional image forming apparatuses are provided with paper detecting means for detecting whether or not paper remains adhered to the belt-shaped rotatable member without being separated therefrom at a separation section of the belt-shaped rotatable member.
For example, JP-A-H11-59962 discloses an image forming apparatus in which a jam sensor is arranged on a paper-introduction side of a fixing device to detect passing of paper that is transported from an intermediate transfer member to the paper-introduction side of the fixing device. Furthermore, separation failure detecting sensor is arranged close to a surface of the intermediate transfer member to detect whether or not paper remains adhered to the surface of the intermediate transfer member without being separated therefrom after a secondary transfer. This separation failure detecting sensor is a reflection-type sensor that irradiates the surface of the intermediate transfer member with light from a light-emitting element and receives the light reflected from the surface of the intermediate transfer member with a light-receiving element; presence of paper remaining adhered to the surface of the intermediate transfer member is detected based on variation in output value of the separation failure detecting sensor. Here, these sensors are set such that, when the jam sensor has not detected passing of paper within a predetermined time period, a jam is judged to have occurred, and when the separation failure detecting sensor has detected presence of paper remaining adhered to the surface of the intermediate transfer member, separation failure is judged to have occurred, and in both cases, operation of the whole apparatus is immediately stopped.
However, with the just-mentioned conventional technology, although it is possible to detect whether or not paper remains adhered to the surface of the intermediate transfer member by use of the separation failure detecting sensor, it is impossible to detect that paper, although it is slightly separated from the intermediate transfer member, is moving toward the paper introduction side of the fixing device in an inappropriate position. Paper in such a case may hit or rub against members and units such as a cleaning member for removing toner remaining on the intermediate transfer member that are arranged on a downstream side of a separation section at which paper is separated, with respect to a paper transportation direction, and this may disturb an image formed on the paper. Furthermore, if paper rushes into the fixing device in an inappropriate position, the paper becomes wrinkled to cause a jam, which is inconvenient. Moreover, the jam sensor arranged on the paper introduction side of the fixing device cannot detect occurrence of a jam even when the wrinkled paper rushes into the fixing device, which is also inconvenient.